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  • 1
    Online Resource
    Online Resource
    Cambridge University Press (CUP) ; 2010
    In:  Proceedings of the International Astronomical Union Vol. 6, No. S272 ( 2010-07), p. 626-627
    In: Proceedings of the International Astronomical Union, Cambridge University Press (CUP), Vol. 6, No. S272 ( 2010-07), p. 626-627
    Abstract: In recent years several in-depth investigations of the three prototypical Of?p stars were undertaken, revealing their peculiar properties. To clarify some of the remaining questions, we have continued our monitoring of the prototypical Of?p trio. HD 108 has now reached its quiescent, minimum-emission state, for the first time in 50–60yrs, while new echelle spectra of HD 148937 confirm the presence in several H and He lines of the 7d variations detected previously only in the Hα line. A new XMM observation of HD 191612 clearly shows that its X-ray emission is not modulated by the orbital period of 1542d, but the high-energy variations are rather compatible with the 538d period of the optical changes - it is thus not of colliding-wind origin but linked to the phenomena responsible for the spectral/photometric variations, though our current MHD simulations remain at odds with the observational properties.
    Type of Medium: Online Resource
    ISSN: 1743-9213 , 1743-9221
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2010
    detail.hit.zdb_id: 2170724-8
    SSG: 16,12
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  • 2
    Online Resource
    Online Resource
    Cambridge University Press (CUP) ; 2010
    In:  Proceedings of the International Astronomical Union Vol. 6, No. S272 ( 2010-07), p. 624-625
    In: Proceedings of the International Astronomical Union, Cambridge University Press (CUP), Vol. 6, No. S272 ( 2010-07), p. 624-625
    Abstract: Oe stars are thought to represent an extension of the Be phenomenon to higher temperatures. Dedicated XMM observations of HD 155806 revealed a surprising X-ray spectrum: soft character, absence of overluminosity, broad X-ray lines. These properties are fully compatible with the wind-shock model, which usually explains the X-rays from “normal”, single O-type stars. In contrast, some other Oe/Be stars display a completely different behaviour at high energies.
    Type of Medium: Online Resource
    ISSN: 1743-9213 , 1743-9221
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2010
    detail.hit.zdb_id: 2170724-8
    SSG: 16,12
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  • 3
    Online Resource
    Online Resource
    Oxford University Press (OUP) ; 2023
    In:  Monthly Notices of the Royal Astronomical Society Vol. 521, No. 2 ( 2023-03-14), p. 2874-2896
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 521, No. 2 ( 2023-03-14), p. 2874-2896
    Abstract: We analyse optical and X-ray spectroscopy of the Of?p star HD 108, known for its strong dipolar magnetic field and its optical line profile variability with a time-scale of 54 ± 3 yrs, interpreted as the stellar rotation period. Optical emission lines have now recovered from their minimum emission state reached in 2007–2008. The variations of the equivalent width of the Hα emission provide constraints on the inclination of the rotation axis (i) and the obliquity of the magnetic axis (β). The best agreement between model and observations is found for (i, β) pairs with i + β ≃ 85° and i ∈ [30°, 55°]. The Balmer emission lines display stochastic variability at the ∼5 per cent level on time-scales of a few days. TESS photometry unveils transient modulations on similar time-scales in addition to prominent red noise variations. A Chandra X-ray observation of December 2021, when the star was at a higher emission level, indicates a slight increase of the flux and a spectral hardening compared to the August 2002 XMM-Newton observation, taken near minimum emission state. Magnetohydrodynamic simulations are used to compute synthetic X-ray spectra. With our current best estimate of the $\dot{M}_{B=0}$ mass-loss rate, the simulated X-ray luminosity and spectral energy distribution agree very well with the observations. Finally, the radial velocities vary on a period of 8.5 yr with a peak-to-peak amplitude of 10–11 km s−1, suggesting orbital motion with an unseen companion of at least 4 M⊙.
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2023
    detail.hit.zdb_id: 2016084-7
    SSG: 16,12
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  • 4
    In: Experimental Astronomy, Springer Science and Business Media LLC, Vol. 54, No. 2-3 ( 2022-12), p. 1307-1337
    Abstract: This article reproduces the contents of the White Paper entitled by the same name submitted to the call issued by the European Space Agency soliciting ideas from the scientific community for the science themes that should be covered during the Voyage 2050 planning cycle. This contribution focus in the investigation of the emergence of life and the role that astronomy has to play in it. Three fundamental areas of activity are identified: [1] measuring the chemical enrichment of the Universe, [2] investigating planet formation and searching for exoplanets with signatures of life and, [3] determining the abundance of amino acids and the chemical routes to amino acid and protein growth in astronomical bodies. This proposal deals with the first two. The building blocks of life in the Universe began as primordial gas processed in stars and mixed at galactic scales. The mechanisms responsible for this development are not well-understood and have changed over the intervening 13 billion years. To follow the evolution of matter over cosmic time, it is necessary to study the strongest (resonance) transitions of the most abundant species in the Universe. Most of them are in the ultraviolet (UV; 950 Å - 3000 Å ) spectral range that is unobservable from the ground; the “missing” metals problem cannot be addressed without this access. Habitable planets grow in protostellar discs under ultraviolet irradiation, a by-product of the accretion process that drives the physical and chemical evolution of discs and young planetary systems. The electronic transitions of the most abundant molecules are pumped by this UV field that is the main oxidizing agent in the disc chemistry and provides unique diagnostics of the planet-forming environment that cannot be accessed from the ground. Knowledge of the variability of the UV radiation field is required for the astrochemical modelling of protoplanetary discs, to understand the formation of planetary atmospheres and the photochemistry of the precursors of life. Earth’s atmosphere is in constant interaction with the interplanetary medium and the solar UV radiation field. The exosphere of the Earth extends up to 35 planetary radii providing an amazing wealth of information on our planet’s winds and the atmospheric compounds. To access to it in other planetary systems, observation of the UV resonance transitions is required. The investigation for the emergence of life calls for the development of large astronomical facilities, including instrumentation in optical and UV wavelengths. In this contribution, the need to develop a large observatory in the optical and in the UV is revealed, in order to complete the scientific goals to investigate the origin of life, inaccessible through other frequencies in the electromagnetic spectrum.
    Type of Medium: Online Resource
    ISSN: 0922-6435 , 1572-9508
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2022
    detail.hit.zdb_id: 2012330-9
    SSG: 16,12
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  • 5
    In: Astrophysics and Space Science, Springer Science and Business Media LLC, Vol. 354, No. 1 ( 2014-11), p. 229-246
    Type of Medium: Online Resource
    ISSN: 0004-640X , 1572-946X
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2014
    detail.hit.zdb_id: 1472548-4
    detail.hit.zdb_id: 2207653-0
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  • 6
    Online Resource
    Online Resource
    Oxford University Press (OUP) ; 2015
    In:  Monthly Notices of the Royal Astronomical Society Vol. 452, No. 3 ( 2015-09-21), p. 2641-2653
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 452, No. 3 ( 2015-09-21), p. 2641-2653
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2015
    detail.hit.zdb_id: 2016084-7
    SSG: 16,12
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